Sending e-mail internally to other network users

Is it possible to send/forward e-mails between network users without sending via the isp?

We use Outlook 2000 and XP pro but don't want to use Instant messenger. The only internet connection is a dial up which is shared by all stations so is inefficient for just forwarding mail to another network station.

click here offer Office Mail which works brilliantly. It costs around £30. POP3 email is downloaded from dial-up or broadband on one P.C. then the other P.C.'s connect to this server via TCP/IP and collect only their mail from it. You can schedule the download of mail automatically every half hour or whatever. Internal mail gets sent through your network immediately. It's dead easy to set up and worth every penny. Tech support is also outstanding.